In answer to your other post, no you can't change onboard graphics chips.
Regarding this post, what slots do you have available to you? PCI-E / PCI / AGP?
You could probably use a Geforce Go setup, but I'm not sure what interfaces they use, or even if they are on-board.
What do you mean by high-end graphics? what do you want to do and at what resolution. You might be better getting a laptop, stripping it, and inserting it into a case.
From what I understand most cards use little power whilst doing 2-d, its only when you try to use the high-end capabilities that they draw power, hence the power saving features are a little redundant if you are planning on high end 3-d intensive applications. I'd imagine that most of the 'go' feature set is based around lower levels of heat dissipation being required.